We propose to investigate the sequence of events that lead to polymorphonuclear leukocyte chemotaxis following the meeting of the cell with Urate Induced Chemotactic Factor and to characterize further the biological and chemical properties of the factor that we have isolated. BIBLIOGRAPHIC REFERENCES: Spilberg, I., Gallacher, A., Mehta, J. M. and Mandell, B.: Urate crystal induced chemotactic factor: Isolation and partial characterization. J. Clin. Invest. 58:815-819, 1976. Tanphaichitr, K., Spilberg, I. and Hahn, B.: Lithium heparin crystals simulating calcium pyrophosphate (CPPD) crystals in synovial fluid. Arth. Rheum. 19:966-967, 1976.